Re: gnu tar 1.19 requires open() with O_DIRECTORY?

[John E. Malmberg]

Eric Blake wrote:
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> According to John E. Malmberg on 2/18/2008 8:46 PM:
> | I have run into a problem: GNU TAR now requires that the open() call
> | support O_DIRECTORY.
>
> Tar is using O_DIRECTORY to close a security hole, and not to directly
> read the directory contents.  And POSIX requires that a directory be
> openable read-only, even though reads on such a fd are allowed to fail.

I could not find that Posix specification on the web, not even a draft.
The X/Open standard which was what was used as a guideline for the VMS 
DECC RTL, does not explicitly make state that open() has that 
requirement, but the description from the error codes implies that 
opening a directory for read should be allowed.

So I can submit a bug report, but I doubt that a fix would show up 
anytime soon, or in older versions.

> Gnulib's replacemente <fcntl.h> should detect platforms that lack
> O_DIRECTORY, and define it to 0 on those platforms.

It did detect it and make the definition.

> The trick now is figuring out why gnulib's <fcntl.h> didn't work for VMS;
> it may also be necessary to provide a replacement open() that can
> 'support' opening directories by using opendir under the hood.

The open() would have to open or dup a file descriptor to the /dev/null 
device to reserve a unique file descriptor, and then something needs to 
map that file descriptor back to the pointer to the *DIR structure.

Now how to implement this in a way that will work with the rest of the 
wrappers?

Regards,
-John
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